The present invention relates generally to actuating devices and more particularly to an actuating device capable of actuating a driven member in a multiple-stage manner by means of a plurality of pistons slidingly operating in a single cylinder.
In the equipment used in the petroleum industry and the chemical industry, in general, there are frequent instances where, for the purpose of shipping by marine transportation or by land transportation, liquids are transferred from large stationary storage tanks constituting sources of the liquids to liquid reservoir tanks for transportation. In such a case, a fixed quantity liquid supplying device which automatically stops its liquid supplying operation when the quantity of liquid supplied reaches a predetermined fixed value is used.
In some instances, the liquid to be supplied to the liquid reservoir tank is a liquid which easily foams or a liquid which generates static electricity at the time of liquid supply because of liquid friction and residual gases within the reservoir tank prior to charging of the liquid thereinto. When such a liquid is to be supplied, the following multiple-stage valve operation is desirable in order to prevent undesirable occurrences such as foaming and generation of static electricity. The liquid is initially supplied through a liquid supply pipeline provided with a shut-off valve with this valve in a suitably throttled state until the supplied liquid level within the reservoir tank rises to a specific height, and, thereafter, the valve is fully opened to increase the flowrate to its maximum value. Furthermore, upon completion of the supplying of the liquid, it is desirable that the valve closing operation also be carried out stepwise by first throttling the liquid flowrate to a certain extent immediately prior to full closing of the shut-off valve in order to prevent water hammering and then to close fully the valve.
Among the devices known heretofore for causing a shut-off valve to undergo multiple stage valve operation, there has been one device in which there is provided, for example, a positioner by which the degree of opening of the shut-off valve is controlled. However, a system for supplying working fluid signals for a multiple-stage shut-off valve to this positioner becomes very complicated, and the entire device becomes expensive.
Furthermore, for the case of a device in which a ball valve is used as a shut-off valve, there has been a device wherein the operations of a plurality of cylinders respectively of different diameters are respectively controlled independently, and the ball valve is operated in multiple stages in opening and closing by the operations of these cylinders. By this arrangement, however, a plurality of cylinders are used, and the ball valve is operated in opening and closing action by the actuating power derived respectively from these cylinders. For this reason, this device has been accompanied by problems such as complicated structure and operational trouble.